System and Method for Verifying a Reference Voltage for Battery Cell Monitoring

ABSTRACT

Systems and methods for verifying a reference voltage within a battery pack are disclosed. In one example, an assessment of a reference voltage is made via a band-gap voltage of a microcontroller. The system and method may be particularly useful determining whether or not the reference voltage has drifted from a desired voltage.

TECHNICAL FIELD

The present description relates to verifying a reference voltage forbattery cell monitoring. In one example, the battery cells are includedin a battery pack provides power to a vehicle.

BACKGROUND AND SUMMARY

A battery pack may comprise a plurality of battery cells. The batterycells may be configured in parallel and series to provide a desiredlevel of battery voltage at a desired amp-hour rating. Battery cellsarranged in series increase battery voltage while battery cells arrangedin parallel increase the amp-hour rating of the battery. When a batterycells are discharged battery cell voltage may decrease. On the otherhand, when battery cells are charged battery cell voltage may increase.Thus, battery voltage can be used as an indication of an amount ofcharge stored in a battery cell so that a battery pack can be charged ordischarged as is prudent, at least under some conditions.

To facilitate battery pack charging and discharging, it is possible todetermine battery cell voltage via an analog to digital converter (ADC).However, an ADC requires a stable reference voltage to accuratelydetermine a voltage of a battery cell. If the reference voltage drifts(e.g., changes) over time, voltage measurements made by an ADC ofbattery cell voltage may degrade in accuracy. Consequently, it may bedifficult to provide an accurate battery cell voltage measurement.Further, it may be difficult to make an accurate determination of totalbattery pack voltage from individual battery cell voltage measurementsmade by an ADC. As a result, it may be desirable to limit battery packcharging and discharging to a reduced level so that the battery packvoltage is within a desired range.

The inventors herein have recognized the above issues and developed anapproach to address them. Specifically, the inventors have developed amethod for verifying a reference voltage for battery cell voltagemonitoring, comprising: referencing a first analog to digital converterto a reference voltage; providing a band-gap voltage from the referencevoltage; and indicating degradation of the reference voltage when theband-gap reference voltage varies from a predetermined voltage range.

By checking a reference voltage which supplies a voltage to an ADC thatmonitors battery cell voltages via a band-gap reference, it may bepossible to determine whether or not the reference voltage is operatingat a desired voltage so that limiting of battery pack charging anddischarging due to a changing reference voltage may be reduced. Thus,when it is determined that the reference voltage is operating at adesired voltage, a higher level of confidence in ADC measurements may beachieved. In one example, the present description provides formonitoring the reference voltage via a band-gap voltage of amicrocontroller. If a voltage of the band-gap voltage varies by morethan a predetermined amount of voltage, a condition of degradation canbe indicated to a battery pack management system. In this way, it ispossible for a plurality of modules to indicate reference voltagedegradation within a battery pack.

The present description may provide several advantages. In particular,the approach can assess reference voltage degradation via an internaltemperature compensated band-gap voltage. Further, the approach canreduce system costs as a second reference voltage is not required toassess the reference voltage.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded schematic view of a battery pack or assembly;

FIG. 2 shows a schematic view of an exemplary battery module;

FIG. 3 shows an exploded schematic view of an exemplary battery cellstack;

FIG. 4 shows an electrical schematic diagram for an example batterypack;

FIG. 5 shows a prophetic example of signals if interest for verifying areference voltage for battery cell monitoring;

FIG. 6 shows a flowchart of a method for verifying a reference voltagefor battery cell monitoring.

DETAILED DESCRIPTION

The present description is related to verifying a reference voltage forbattery cell monitoring. In one example, the battery cells may beincluded in a battery pack as illustrated in FIG. 1. Battery cells suchas those illustrated in FIGS. 2-3 may be combined as shown in FIG. 1.The reference voltage may be configured as an ADC reference voltageaccording the battery pack electrical schematic of FIG. 4. A graphicalexample of one way to evaluate and indicate degradation of a referencevoltage is shown in FIG. 5. In the method of FIG. 6, a band-gapreference voltage is evaluated in view of a desired band-gap voltage todetermine whether or not the reference voltage is at a desired voltage.

FIG. 1 shows an exploded view of a battery assembly 1. The batteryassembly may include a cover 10, coupling devices 12, a first coolingsubsystem 14 (e.g., cold plate), a plurality of battery cell modules 16,a second cooling subsystem 18 (e.g., cold plate), and a tray 20. Thecover may be attached to the tray via a suitable coupling device (e.g.,bolts, adhesive, etc.,) to form a housing surrounding the couplingdevices, the cooling subsystems, and the battery modules, whenassembled.

The battery cell modules 16 may include a plurality of battery cellsconfigured to store energy. Although a plurality of battery modules areillustrated, it will be appreciated that in other examples a singlebattery module may be utilized. Battery cell modules 16 may beinterposed between the first cooling subsystem 14 and the second coolingsubsystem 18, where the battery modules are positioned with theirelectrical terminals on a side 21 facing out between the coolingsubsystems.

Each battery module may include a first side 23 and a second side 25.The first and the second side may be referred to as the top and bottomside, respectively. The top and bottom sides may flank the electricalterminals, discussed in greater detail herein with regard to FIGS. 2-3.In this example, the top side of each battery module is positioned in acommon plane in the battery assembly. Likewise, the bottom side of eachbattery module is positioned in another common plane in the batteryassembly. However, in other examples only the top side or the bottomside of each battery module may be positioned in a common plane. In thisway, the cooling subsystems may maintain direct contact with the topsides and the bottom sides of the battery modules to increase heattransfer and improve cooling capacity, as described in further detailherein, wherein the cooling subsystems and the battery modules may be inface-sharing contact. Additional details of an exemplary battery moduleare described herein with regard to FIGS. 2-3. In alternate examples,only one of the cooling subsystems may be included in battery assembly1, such as an upper cooling subsystem (subsystem 14 in this example).Moreover, the position, size, and geometry of the first and secondcooling subsystems are exemplary in nature. Thus, the position, size,and/or geometry of the first and/or second cooling subsystems may bealtered in other examples based on various design parameters of thebattery assembly.

Battery assembly 1 may also include an electrical distribution module 33(EDM), monitor and balance boards 35 (MBB), and a battery control module37 (BCM). Voltage of battery cells in battery cell modules 16 may bemonitored and balanced by MBBs that are integrated onto battery cellmodules 16. Balancing battery cells refers to equalizing voltagesbetween a plurality of battery cells in a battery cell stack. Further,battery cell voltages between battery cell stacks can be equalized. MBBsmay include a plurality of current, voltage, and other sensors. The EDMcontrols the distribution of power from the battery pack to the batteryload. In particular, the EDM contains contactors for coupling highvoltage battery power to an external battery load such as an inverter.The BCM provides supervisory control over battery pack systems. Forexample, the BCM may control ancillary modules within the battery packsuch as the EDM and cell MBB. Further, the BCM may be comprised of amicrocontroller having random access memory, read only memory, inputports, real time clock, output ports, and a controller area network(CAN) port for communicating to systems outside of the battery pack aswell as to MBBs and other battery pack modules.

FIG. 2 shows an exemplary battery module 200 that may be included in theplurality of battery cell modules 16, shown in FIG. 1. Battery module200 may include a battery cell stack having a plurality of stackedbattery cells and output terminals 201. The stacked arrangement allowsthe battery cells to be densely packed in the battery module.

FIG. 3 shows an exploded view of a portion of an exemplary battery cellstack 300. As shown the battery cell stack is built in the order of ahousing heat sink 310, battery cell 312, compliant pad 314, battery cell316, and so on. However, it will be appreciated that other arrangementare possible. For example, the battery cell stack may be built in theorder of a housing heat sink, battery cell, housing heat sink, etc.Further in some examples, the housing heat sink may be integrated intothe battery cells.

Battery cell 312 includes cathode 318 and anode 320 for connecting to abus bar (not shown). The bus bar routes charge from one batter cell toanother. A battery module may be configured with battery cells that arecoupled in series and/or parallel. Bus bars couple like battery cellterminals when the battery cells are combined in parallel. For example,the positive terminal of a first battery cell is coupled to the positiveterminal of a second battery cell to combine the battery cells inparallel. Bus bars also couple positive and negative terminal of batterycell terminals when it is desirable to increase the voltage of a batterymodule. Battery cell 312 further includes prismatic cell 324 thatcontains electrolytic compounds. Prismatic cell 324 is in thermalcommunication with cell heat sink 326. Cell heat sink 326 may be formedof a metal plate with the edges bent up 90 degrees on one or more sidesto form a flanged edge. In the example of FIG. 3, two opposing sidesinclude a flanged edge. However, other geometries are possible. Batterycell 312 is substantially identical to battery cell 316. Thereforesimilar parts are labeled accordingly. Battery cells 312 and 316 arearranged with their terminals in alignment and exposed. In batterymodule 200 shown in FIG. 2 the electric terminals are coupled to enableenergy to be extracted from each cell in the battery module. Returningto FIG. 3, compliant pad 314 is interposed between battery cell 312 andbattery cell 316. However, in other examples the compliant pad may notbe included in the battery cell stack.

Housing heat sink 310 may be formed by a metal plate having a base 328with the edges bent up 90 degrees on one or more sides to form a flangededge. In FIG. 3 longitudinally aligned edge 330 and vertically alignededges 332 are bent flanged edges. As depicted, the housing heat sink issized to receive one or more battery cells. In other words, one or morebattery cells may be positioned within base 328. Thus, the flanged edgesof the battery cells may be in contact with housing heat sink andunderside 329 of battery cell 312 may be in contact with the base of thehousing heat sink, facilitating heat transfer.

One of the longitudinally aligned edges 332 of the housing heat sink 310may form a portion of the top side 202 of battery module 200, as shownin FIG. 2. Similarly, one of the longitudinally aligned edges 332 mayform a portion of the bottom side of the battery module. Thus, thelongitudinally aligned edges of the housing heat sink may be in contactwith the first and the second cooling subsystems to improve heattransfer. In this way, heat may be transferred from the battery cells tothe exterior of the battery module.

The battery cells may be strapped together by binding bands 204 and 205.The binding bands may be wrapped around the battery cell stack or maysimply extend from the front of the battery cell stack to the back ofthe battery cell stack. In the latter example, the binding bands may becoupled to a battery cover. In other examples, the binding bands may becomprised of threaded studs (e.g., metal threaded studs) that are boltedat the ends. Further, various other approaches may be used to bind thecells together into the stack. For example, threaded rods connected toend plates may be used to provide the desired compression. In anotherexample, the cells may be stacked in a rigid frame with a plate on oneend that could slide back and forth against the cells to provide thedesired compressive force. In yet other examples, rods held in place bycotter pins may be used to secure the battery cells in place. Thus, itshould be understood that various binding mechanisms may be used to holdthe cell stack together, and the application is not limited to metal orplastic bands. Cover 206 provides protection for battery bus bars (notshown) that route charge from the plurality of battery cells to outputterminals of the battery module.

The battery module may also include a front end cover 208 and a rear endcover 210 coupled to the battery cell stack. The front and rear endcovers include module openings 26. However, in other examples the moduleopenings may be included in a portion of the battery module containingbattery cells.

Referring now to FIG. 4, a schematic diagram for controlling batterypack output is shown. In this example, battery pack 400 includes twobattery cell modules 402 and 418 as indicated by the dashed lines.Further, current sense module 444 and battery control or managementmodule 438 are shown.

Battery cells 416 and 432 are shown identically configured and areconnected in series. However, battery cell modules may be configuredwith different numbers of battery cells, and the battery cells may beconfigured differently if desired. For example, battery cells 416 and432 are comprised of eight battery cells each. Four of the battery cellsare arranged in series. Further, the four battery cells are arranged inparallel with four other battery cells that are arranged in series. Inthis configuration, each battery module 402 and 418 outputs a voltagethat is related to the number of battery cells connected in series aswell as the individual voltage output of each battery cell. And, asdiscussed above, the current capacity or amp-hour rating of the batterymodule may be related to the number of battery cells connected inparallel. As the number of battery cells arranged in parallel increases,the battery module amp-hour rating increases. As the number of batterycells arranged in series increases, the output voltage of the batterymodule increases. Thus, the voltage output of a battery pack can beincreased or decreased by changing the number of battery cells arrangedin a series connection. Likewise, the battery pack amp-hour rating maybe increased or decreased by changing the number of battery cellsarranged in parallel. Therefore, in this example, the battery packvoltage may be increased by adding additional battery cells in serieswith the battery cells of battery cell modules 416 and 432.Alternatively, the battery module amp-hour rating may be increased byadding more battery cells in parallel to battery cells 416 and 432.

Battery cell modules 402 may be configured to include a high voltage busand a low voltage bus. The high voltage bus may be isolated from the lowvoltage bus to reduce ground loops and electrical noise within thebattery pack. The battery cells and power electronics can be included ona portion of the battery cell module 402 that are in communication withthe high voltage bus. Low level electronics are in communication withthe low voltage bus.

Battery cell modules 402 and 418 include input switches 404 and 420 forselectively coupling ADCs 406 and 422 to battery cells 416 and 432respectively. MCUs 414 and 430 control the state of switches 404 and 420by way of digital outputs from the respective MCUs. Input switches 404and 420 are configured such that ADCs 406 and 422 may be coupled toindividual battery cells to measure battery cell voltage without beinginfluenced by the voltage of battery cells that may be placed in serieswith the battery cell being measured. In one example, each MCU 414 and430 may couple each series connected battery cell to respective ADCs 406and 422. When battery cells are coupled in parallel, input switches 404and 420 couple ADCs 406 and 422 to the battery cells of a battery modulethat are coupled in parallel. Thus, each ADC coupled to a battery cellstack may be configured to measure the voltage of one or more batterycells coupled in parallel within the respective battery cell stack.

ADCs 406 and 422 are configured as high resolution (e.g., 12 or 16 bitresolution ADCs) devices that are external or off chip from MCUs 414 and430 although ADCs may be on chip in other examples and may havedifferent resolutions (e.g., 8 bit resolution). In one example, ADCs 406and 422 communicate with MCUs 414 and 430 respectively by way of SPIports. The SPI ports are used to transfer battery cell voltages to eachMCU as the individual MCUs command input switches 404 and 420 to cyclethrough battery cells 416 and 432 respectively. By cycling through theswitches, individual series battery cells are coupled to ADCs 406 and422 for determining battery cell voltages.

Reference voltage sources 408 and 424 provide a high accuracy referencevoltage to ADCs 406 and 422, respectively. In addition, referencevoltage sources 408 and 424 provide power to generate band-gap voltagesinternal to MCUs 414 and 430, respectively. The band-gap voltageinternal to MCU 414 is provided by band-gap voltage source 412 and isrelated to the output of reference voltage 408, and the band-gap voltageinternal to MCU 430 is provided by band-gap voltage source 428 and isrelated to the output reference voltage 424. Consequently, if thereference voltage provided by reference voltage source 408 varies, theband-gap voltage provided by band-gap voltage source 412 to MCU 414varies. Likewise, if the reference voltage provided by reference voltagesource 424 varies, the band-gap voltage provided by band-gap voltagesource 428 to MCU 430 varies.

ADCs 410 and 426 are lower resolution (e.g., 8 bit resolution) devicesthat are integrated to MCUs 414 and 430. In alternate examples, ADCs 410and 426 may be of higher resolution (e.g., 12 or 16 bit resolution) andexternal from MCUs 414 and 430. ADCs 410 and 426 are configured tomeasure the series voltage provided by battery cells 416 and 432 for therespective battery cell stacks 402 and 418. For example, ADC 410 isconfigured to measure the voltage provided by the series combination offour battery cells coupled in parallel to four other battery cells, thebattery cells indicated at 416. Thus, the ADC of an MBB is configured tomeasure the series combination of battery cells of a battery module. Ofcourse, an ADC of a MBB coupled to a battery module may be configured tomeasure the voltage of additional or fewer battery cells than the fourbattery cells shown in FIG. 4. Further, as discussed above, the seriescombination of battery cells 416 acts to increase the output voltage ofthe battery module 402. In one example, MCU 414 includes instructionsfor comparing a sum of battery cell voltages determined from ADC 406 toa voltage of the battery cell module 402 determined from ADC 410. Inparticular, MCU 414 includes instructions for determining a differencebetween the sum of individual battery cell voltages determined from ADC406 from an individual battery cell voltage measurement from ADC 410.

ADCs 410 and 426 are further configured to measure and monitor band-gapreference voltages provided by band-gap reference voltage sources 412and 428. ADC 410 is provided a reference voltage from reference voltagesource 408. Similarly, ADC 426 is provided a reference voltage fromreference voltage source 424. Thus, the measurements of band-gap voltageprovided by ADCs 410 and 426 are referenced to the reference voltagefrom reference voltage sources 408 and 424, respectively.

MCUs 414 and 430 control input switches 404 and 420 as well as ADCs 406and 410, 422, and 426. Further, MCUs 410 and 430 may store therespective battery voltages to memory and perform arithmetic and logicaloperations on battery voltage data captured by ADCs 406, 410, 422, and426. MCUs 414 and 430 also have an internal temperature sensor so themeasured temperature of the MCU can be used to adjust for temperaturedrift of the internal band-gap voltage.

BCM 438 communicates with MCUs 414 and 430 of battery cell modules 402and 418 by way of CAN bus 440; however, other types of communicationlinks are also possible and anticipated. BCM 438 may acquire batteryvoltages and status indicators (e.g., flags that indicate degradation ofan ADC, degradation of a reference voltage source, battery cell, or MCU)from battery cell modules 402 and 418. BCM 438 also communicates withEDM 442 via hardwired digital inputs and outputs for opening and closingcontactors 450 and 448. In an alternative example, BCM 438 maycommunicate to EDM 442 via CAN 440 for sending instructions to closecontactors 450 and 448 when it is determined to couple battery cellstacks 402 and 432 to the battery load or source. Contactors 450 and 448act as electrically controlled switches and do not interrupt shortcircuit current without instruction from BCM 438. In one example,contactors 450 and 448 are normally open and include a closing coil andmetallic contacts that may be engaged and disengaged with metalliccurrent carrying conductors by operating the closing coil. In oneexample, the contactors open by physically moving apart. In otherexamples where less power is provided by the battery pack, the outputcontactor may be a silicon based contactor such as a FET or bi-polartransistor, for example.

CSM 444 includes an ADC 446 for measuring battery pack current on thebattery side of contactors 450 and 448. Current shunt 472 provides avoltage that is proportional to current flow entering or exiting thebattery pack to a microcontroller within CSM 444. The CSMmicrocontroller converts battery pack current into digital data via ADC446. The CSM microcontroller transmits current data to BCM 438 via CANbus 440. BCM 438 also communicates with a vehicle controller via CAN bus460. BCM 438 may communicate a variety of battery related information toa vehicle controller via CAN bus 460. For example, BCM 438 can send anindication of available battery current capacity and/or an indication ofbattery current sinking or sourcing capacity. Fuse 462 provides currentlimiting protection to the battery pack.

Thus, the system of FIGS. 1-4 provides for a system for assessing ananalog to digital converter reference voltage for monitoring a batterycell voltage, comprising: a reference voltage; a first analog to digitalconverter, the first analog to digital converter in electricalcommunication with the reference voltage, the first analog to digitalconverter configured to sample a voltage of at least one battery cell;and a controller, the controller in electrical communication with thefirst analog to digital converter, the controller including a secondanalog to digital converter and an internal band-gap voltage, theinternal band-gap voltage responsive to the reference voltage, thecontroller including instructions for monitoring the internal band-gapvoltage to verify the reference voltage is a desired voltage. The systemincludes where the first analog to digital converter is external to thecontroller, and where the controller includes further instructions forsetting a flag to indicate degradation of the reference voltage to abattery pack management system. The system includes where the secondanalog to digital converter is configured to monitor the internalband-gap voltage, and where the controller includes further instructionsfor comparing a voltage of the internal band-gap voltage to apredetermined voltage range. The system includes where the second analogto digital converter is integrated in the controller and is furtherconfigured to monitor a voltage of a plurality of battery cells. Thesystem includes where the controller includes further instructions forcomparing a sum of individual battery cell voltage measurements from thefirst analog to digital converter to a measurement of a single voltagefrom the second analog to digital converter, the single voltage from thesecond analog to digital converter provided via a plurality of batterycells. The system includes where the instructions for comparing a sum ofindividual battery cell voltage measurements from the first analog todigital converter to a measurement of a single voltage from the secondanalog to digital converter includes determining a difference betweenthe sum of individual battery cell voltage measurements from the firstanalog to digital converter and a single sample output from the secondanalog to digital converter. The system includes where a voltage of theinternal band-gap voltage is based on the reference voltage.

The system of FIGS. 1-4 further provides for a system for assessing asystem for assessing an analog to digital converter reference voltagefor monitoring a battery cell voltage, comprising: a reference voltage;a first analog to digital converter, the first analog to digitalconverter in electrical communication with the reference voltage, thefirst analog to digital converter configured to sample a voltage of atleast one battery cell, the first analog to digital converter configuredto determine a voltage of the at least one battery cell referenced withrespect to the reference voltage; and a controller, the controller inelectrical communication with the first analog to digital converter, thecontroller including a second analog to digital converter and aninternal band-gap voltage, the internal band-gap voltage responsive tothe reference voltage, the second analog to digital converter configuredto determine a reference voltaged with respect to the reference voltage,the controller including instructions for monitoring the internalband-gap voltage via the second analog to digital converter to verifythe reference voltage is a desired voltage. The system includes wherethe controller includes further instructions for indicating a conditionof degradation of the reference voltage to a battery pack managementsystem. The system includes where the instructions for monitoring theinternal band-gap voltage include instructions for comparing a voltageof the internal band-gap voltage to a predetermined voltage range. Thesystem includes where the predetermined voltage range varies with atemperature of a battery pack, the battery pack including the controllerand the at least one battery cell. The system includes where thereference voltage is a voltage greater than the internal band-gapvoltage, and where the internal band-gap voltage is based on thereference voltage, and where the internal band-gap voltage is configuredto vary as the reference voltage varies. The system includes where thecontroller includes further instructions for comparing a sum ofindividual battery cell voltage measurements from the first analog todigital converter to a measurement of a single voltage from the secondanalog to digital converter, the sum of individual battery cell voltagemeasurements referenced with respect to the reference voltage, thesingle voltage of the second analog to digital converter referenced withrespect to the reference voltage and related to a plurality of batterycells. The system includes where the first analog to digital converteris external of the controller, and where that at least one battery cellis a lithium-ion battery cell.

Referring now to FIG. 5, a prophetic example of signals of interest forverifying a reference voltage for battery cell monitoring is shown. Theillustrated signals may be available from the system shown in FIGS. 1-4executing the method of FIG. 6.

The first plot from the top of FIG. 5 represents a reference voltagewith respect to time. The Y axis represents voltage, and voltageincreases in the direction of the Y axis arrow. The X axis representstime, and time increases in the direction of the X axis arrow.Horizontal line 502 represents a first threshold voltage for comparingagainst the voltage output from the reference voltage source. Horizontalline 504 represents a second threshold voltage for comparing against thevoltage output from the reference voltage source. In one example, thearea between horizontal line 502 and horizontal line 504 indicates adesired range of voltage output for the reference voltage source. Thevalues represented by horizontal lines 502 and 504 can be varied withbattery operating conditions if desired. For example, the voltage rangebetween horizontal line 502 and 504 can be increased as a temperature ofa battery pack increases. In another example, the voltage range betweenhorizontal line 502 and 504 can be adjusted based on the chemistry ofthe battery cell being measured by the ADC.

The second plot from the top of FIG. 5 represents band-gap voltageinternal to a microcontroller of a battery cell stack monitoring andbalancing board. The Y axis represents voltage, and voltage increases inthe direction of the Y axis arrow. The X axis represents time, and timeincreases in the direction of the X axis arrow. Horizontal line 506represents a first threshold voltage for comparing against the voltageoutput from the band-gap voltage source. Horizontal line 508 representsa second threshold voltage for comparing against the voltage output fromthe band-gap voltage source. In one example, the area between horizontalline 506 and horizontal line 508 indicates a desired range of voltageoutput for the band-gap voltage source. The values represented byhorizontal lines 506 and 508 can be varied with battery operatingconditions if desired. For example, the voltage range between horizontalline 506 and 508 can be increased as a temperature of a battery packincreases. In another example, the voltage range between horizontal line506 and 508 can be adjusted based on the specifications of themicrocontroller generating the band-gap voltage.

The sequence of FIG. 5 begins at T₀ and proceeds to the right. At timeT₀, the reference voltage is in its desired voltage range betweenhorizontal lines 502 and 504. The band-gap voltage produced by aband-gap voltage source within a microcontroller configured to monitorbattery cells is also in its desired voltage range between horizontallines 506 and 508. Therefore, the reference voltage degradation flag isnot asserted.

Between times T₁ and T₂ the reference voltage begins to drift to a lowervoltage. The reference voltage may drift to a lower voltage if currentdemand from the reference voltage increases beyond a desired amount. Theband-gap voltage is also shown drifting to a lower voltage since theband-gap voltage is related to the reference voltage. The referencevoltage degradation flag remains not asserted between times T₁ and T₂.

At time T₂, the reference voltage and the band-gap voltage fall tolevels less than the desired voltage range shown by horizontal lines502-504 and horizontal lines 506-508. The ADC on the microcontrollerchip (e.g., ADC 410 of FIG. 4) converts the band-gap voltage to adigital number that represents the band-gap voltage. The microcontroller(e.g., MCU 414 of FIG. 4) compares the digital number from the ADC to afirst upper voltage limit and a second lower voltage limit anddetermines that the band-gap voltage is out of range (e.g., lower thanthe desired voltage range). Since the band-gap voltage is related to thereference voltage it can be judged by the microcontroller that thereference voltage is degraded. Therefore, the reference voltagedegradation flag is asserted by the microcontroller shortly after T₂.

Between time T₂ and T₃ a break in the X axis is shown to indicated abreak in time. Further, the voltage degradation flag is cleared and thereference voltage and band-gap voltage are once again within the desiredvoltage ranges defined by 502-504 and 506-508 at time T₃.

Between times T₄ and T₅ the reference voltage begins to drift to ahigher voltage. The reference voltage may drift to a higher voltage ifthe voltage regulator of the reference voltage degrades or if a voltageis added to the reference voltage. The band-gap voltage is also showndrifting to a higher voltage since the band-gap voltage is related tothe reference voltage. The reference voltage degradation flag remainsnot asserted between times T₄ and T₅.

At time T₅, the reference voltage and the band-gap voltage rise tolevels greater than the desired voltage range shown by horizontal lines502-504 and horizontal lines 506-508. The ADC on the microcontrollerchip (e.g., ADC 410 of FIG. 4) converts the band-gap voltage to adigital number that represents the band-gap voltage. The microcontroller(e.g., MCU 414 of FIG. 4) compares the digital number from the ADC to afirst upper voltage limit and a second lower voltage limit anddetermines that the band-gap voltage is out of range (e.g., greater thanthe specified voltage range). Since the band-gap voltage is related tothe reference voltage it can be judged by the microcontroller that thereference voltage is degraded. Therefore, the reference voltagedegradation flag is asserted by the microcontroller at T₅. In oneexample, the reference voltage degradation flag may remain asserted evenif the band-gap voltage returns to the desired voltage range. Further,in some examples the reference voltage degradation flag may not beasserted unless the band-gap voltage is out of the desired voltage rangefor a predetermined amount of time. In this way, there may be someflexibility to asserting the reference voltage degradation flag.

Referring now to FIG. 6, a method for assessing degradation of areference voltage that is in electrical communication with at least onebattery cell is shown. The method of FIG. 6 is executable viainstructions included in a microcontroller such as MCU 414 of FIG. 5.

At 602, method 600 judges whether or not time since sleep mode isgreater than a threshold amount of time. In one example, during sleepmode the battery does not sink or source current to an external load.Further, selected systems within the battery may enter state of lowercapability (e.g., systems may monitor battery conditions with lessfrequency) and lower power consumption. For example, the reference andband-gap voltages may be deactivated during sleep mode. Consequently,when the battery pack exits sleep mode a predetermined amount of timemay be required before the reference voltage and band-gap voltagestabilize to a desired voltage. If the time since sleep mode is notgreater than a threshold amount of time method 600 proceeds to exit.Otherwise, method 600 proceeds to 604.

At 604, method 600 determines battery pack operating conditions. Batterypack operating conditions may include, but are not limited to, a batterypack temperature, band-gap voltages of selected microcontrollers,reference voltages of selected MBBs, and battery pack status. Method 600proceeds to 606 after battery pack operating conditions are determined.

At 606, method 600 judges whether or not a band-gap voltage of aselected microcontroller is greater than a first threshold voltage. Inone example, the band-gap voltage is measured via an ADC on themicrocontroller chip (e.g., ADC 410 of MCU 414 as shown in FIG. 4). Thefirst threshold voltage is stored in the microcontroller and may beadjusted for battery pack operating conditions. For example, the firstthreshold voltage may increase for increasing battery pack temperatures.If the band-gap voltage is greater than the first threshold voltage,method 600 proceeds to 610. Otherwise, method 600 proceeds to 608.

At 608, method 600 judges whether or not a band-gap voltage of aselected microcontroller is less than a second threshold voltage. Thesecond threshold voltage is stored in the microcontroller and may beadjusted for battery pack operating conditions. For example, the secondthreshold voltage may decrease for increasing battery pack temperatures.If the band-gap voltage is less than the first threshold voltage, method600 proceeds to 610. Otherwise, method 600 proceeds to exit.

At 610, method 600 sets the reference voltage degradation flag. Thereference voltage degradation flag may be provided from a MBBmicrocontroller to a battery management system such as a BCM to indicatedegradation of a reference voltage of a particular MBB. Thus, aplurality of reference voltage degradation flags may be supplied to aBCM when a battery pack is comprised of a plurality of MBBs. If areference voltage degradation flag is asserted the BCM may takemitigating actions, if desired. For example, the BCM may limit batterypack charging and discharging such that the battery pack may not becharged or discharged to full capacity. In another example, the BCM mayindicate a condition of degradation to an external controller and openoutput contactors to remove battery power from the vehicle. Method 600proceeds to exit after the reference voltage degradation flag isasserted.

It should be noted that the reference voltage degradation flag mayremain asserted until cleared by a technician. In other examples, thereference voltage degradation flay may be cleared after the referencevoltage is within a desired voltage range for a predetermined amount oftime.

Thus, the method of FIG. 6 provides for a method for verifying areference voltage for battery cell voltage monitoring, comprising:referencing a first analog to digital converter to a reference voltage;providing a band-gap voltage from the reference voltage; and indicatingdegradation of the reference voltage when the band-gap reference voltagevaries from a predetermined voltage range. In this way, the referencevoltage may be monitored. The method further comprises referencing asecond analog to digital converter to the band-gap voltage andmonitoring the band-gap voltage via the second analog to digitalconverter. The method includes where the band-gap voltage is internal toa microcontroller and where the reference voltage is external of themicrocontroller. The method also includes where the predeterminedvoltage range varies with a temperature of a battery pack, and where thebattery pack includes the reference voltage. In yet another example, themethod includes where indicating degradation of the reference voltageincludes notifying a battery pack management system. The method alsoincludes where a voltage of the band-gap voltage is less than a voltageof the reference voltage.

As will be appreciated by one of ordinary skill in the art, methoddescribed in FIG. 6 may be represented by instructions for a controllerand may be represented by one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various steps or functionsillustrated may be performed in the sequence illustrated, in parallel,or in some cases omitted. Likewise, the order of processing is notnecessarily required to achieve the objects, features, and advantagesdescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated steps,functions, or methods may be repeatedly performed depending on theparticular strategy being used.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A system for assessing an analog to digital converter referencevoltage for monitoring a battery cell voltage, comprising: a referencevoltage; a first analog to digital converter, the first analog todigital converter in electrical communication with the referencevoltage, the first analog to digital converter configured to sample avoltage of at least one battery cell; and a controller, the controllerin electrical communication with the first analog to digital converter,the controller including a second analog to digital converter and aninternal band-gap voltage, the internal band-gap voltage responsive tothe reference voltage, the controller including instructions formonitoring the internal band-gap voltage to verify the reference voltageis a desired voltage.
 2. The system of claim 1, where the first analogto digital converter is external to the controller, and where thecontroller includes further instructions for setting a flag to indicatedegradation of the reference voltage to a battery pack managementsystem.
 3. The system of claim 2, where the second analog to digitalconverter is configured to monitor the internal band-gap voltage, andwhere the controller includes further instructions for comparing avoltage of the internal band-gap voltage to a predetermined voltagerange.
 4. The system of claim 3, where the second analog to digitalconverter is integrated in the controller and is further configured tomonitor a voltage of a plurality of battery cells.
 5. The system ofclaim 1, where the controller includes further instructions forcomparing a sum of individual battery cell voltage measurements from thefirst analog to digital converter to a measurement of a single voltagefrom the second analog to digital converter, the single voltage from thesecond analog to digital converter provided via a plurality of batterycells.
 6. The system of claim 5, where the instructions for comparing asum of individual battery cell voltage measurements from the firstanalog to digital converter to a measurement of a single voltage fromthe second analog to digital converter includes determining a differencebetween the sum of individual battery cell voltage measurements from thefirst analog to digital converter and a single sample output from thesecond analog to digital converter.
 7. The system of claim 1, where avoltage of the internal band-gap voltage is based on the referencevoltage.
 8. A system for assessing an analog to digital converterreference voltage for monitoring a battery cell voltage, comprising: areference voltage; a first analog to digital converter, the first analogto digital converter in electrical communication with the referencevoltage, the first analog to digital converter configured to sample avoltage of at least one battery cell, the first analog to digitalconverter configured to determine a voltage of the at least one batterycell referenced with respect to the reference voltage; and a controller,the controller in electrical communication with the first analog todigital converter, the controller including a second analog to digitalconverter and an internal band-gap voltage, the internal band-gapvoltage responsive to the reference voltage, the second analog todigital converter configured to determine a reference voltaged withrespect to the reference voltage, the controller including instructionsfor monitoring the internal band-gap voltage via the second analog todigital converter to verify the reference voltage is a desired voltage.9. The system of claim 8, where the controller includes furtherinstructions for indicating a condition of degradation of the referencevoltage to a battery pack management system.
 10. The system of claim 8,where the instructions for monitoring the internal band-gap voltageinclude instructions for comparing a voltage of the internal band-gapvoltage to a predetermined voltage range.
 11. The system of claim 10,where the predetermined voltage range varies with a temperature of abattery pack, the battery pack including the controller and the at leastone battery cell.
 12. The system of claim 8, where the reference voltageis a voltage greater than the internal band-gap voltage, and where theinternal band-gap voltage is based on the reference voltage, and wherethe internal band-gap voltage is configured to vary as the referencevoltage varies.
 13. The system of claim 8, where the controller includesfurther instructions for comparing a sum of individual battery cellvoltage measurements from the first analog to digital converter to ameasurement of a single voltage from the second analog to digitalconverter, the sum of individual battery cell voltage measurementsreferenced with respect to the reference voltage, the single voltage ofthe second analog to digital converter referenced with respect to thereference voltage and related to a plurality of battery cells.
 14. Thesystem of claim 8, where the first analog to digital converter isexternal of the controller, and where that at least one battery cell isa lithium-ion battery cell.
 15. A method for verifying a referencevoltage for battery cell voltage monitoring, comprising: referencing afirst analog to digital converter to a reference voltage; providing aband-gap voltage from the reference voltage; and indicating degradationof the reference voltage when the band-gap reference voltage varies froma predetermined voltage range.
 16. The method of claim 15 furthercomprising referencing a second analog to digital converter to theband-gap voltage and monitoring the band-gap voltage via the secondanalog to digital converter.
 17. The method of claim 16, where theband-gap voltage is internal to a microcontroller and where thereference voltage is external of the microcontroller.
 18. The method ofclaim 16, where the predetermined voltage range varies with atemperature of a battery pack, and where the battery pack includes thereference voltage.
 19. The method of claim 15, where indicatingdegradation of the reference voltage includes notifying a battery packmanagement system.
 20. The method of claim 15, where a voltage of theband-gap voltage is less than a voltage of the reference voltage.